Use of a sol–gel conversion coating for aluminum corrosion protection

• Published in: Surface & coatings technology 2001-05, Vol.140 (1), p.44-50
• Main Authors: Yang, X.F., Tallman, D.E., Gelling, V.J., Bierwagen, G.P., Kasten, L.S., Berg, J.
• Format: Article
• Language: English
• Subjects: Aluminum; Applied sciences; Corrosion; Corrosion prevention; Corrosion protection; Exact sciences and technology; Metals. Metallurgy; Sol–gel
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/S0257-8972(01)01002-7

In this study, the behavior of a sol–gel conversion coating alone and in combination with a polyurethane unicoat (TT-P-2756, self-priming topcoat) on Al 2024-T3 alloy was investigated under immersion in dilute Harrison's solution [3.5 g/l (NH 4) 2SO 4, 0.5 g/l NaCl]. The sol–gel coating consisted of SiO 2 and ZrO 2 with a ratio of 3.4:1. The evolution of the coating system under immersion was followed by atomic force microscopy (AFM), scanning electronic microscopy (SEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). It was found that though pitting corrosion and degradation products on the sol–gel single coating surface were observed after 2 days of immersion, further pitting corrosion ceased after a few days of immersion. Under-coating blisters in the sol–gel plus polyurethane topcoat system were found at 4 weeks of immersion, after which no further increase in size of the blisters was observed. It is conjectured that aluminum oxide and silicon oxide may form a stable mixed oxide barrier layer at the interface after initial corrosion, which prohibits further pitting corrosion development.